Amide-imide polymers are a relatively new class of substances known for their solubility in nitrogen-containing solvents when in the largely-polyamide form. They can be heat treated to the imidized form producing insoluble, inflexible, tough, heat-resistant dielectric materials useful as electric insulating coatings and impregnating material. Their use in molding applications has been limited in the past because the more temperature-resistant polymers soften at too high a temperature to be practically molded and also because a preliminary lengthy heat and solvent treatment is required, prior to molding, to circumvent friability and poor mold-release properties in the fabricated article. Now it has been found that amide-imide copolymers which are prepared from mixtures of largely- or wholly-aromatic primary diamines form molding powders which combine the properties of a simplified heat treatment prior to molding and excellent thermal stability and mold release characteristics in the molded article in addition to remarkably improved hot-flow characteristics of the softened material during the molding process.